Avoid racy depmodes with universal builds.

* m4/depend.m4 (_AM_DEPENDENCIES): If universal builds are used,
avoid racy depmodes.
* lib/depcomp: Ignore `-arch' argument for makedepend depmode.
Report by Bruno Haible, analysis by Bruno Haible, Peter O'Gorman,
and Eric Blake.

Signed-off-by: Ralf Wildenhues <Ralf.Wildenhues@gmx.de>

1 files changed, 14 insertions, 0 deletions

diff --git a/m4/depend.m4 b/m4/depend.m4
index 451312a37..efe86436a 100644
--- a/m4/depend.m4
+++ b/m4/depend.m4
@@ -63,6 +63,16 @@ AC_CACHE_CHECK([dependency style of $depcc],
   if test "$am_compiler_list" = ""; then
      am_compiler_list=`sed -n ['s/^#*\([a-zA-Z0-9]*\))$/\1/p'] < ./depcomp`
   fi
+  am__universal=false
+  m4_case([$1], [CC],
+    [case " $depcc " in #(
+     *\ -arch\ *\ -arch\ *) am__universal=true ;;
+     esac],
+    [CXX],
+    [case " $depcc " in #(
+     *\ -arch\ *\ -arch\ *) am__universal=true ;;
+     esac])
+
   for depmode in $am_compiler_list; do
     # Setup a source with many dependencies, because some compilers
     # like to wrap large dependency lists on column 80 (with \), and
@@ -87,6 +97,10 @@ AC_CACHE_CHECK([dependency style of $depcc],
     am__obj=sub/conftest.${OBJEXT-o}
     am__minus_obj="-o $am__obj"
     case $depmode in
+    gcc)
+      # This depmode causes a compiler race in universal mode.
+      test "$am__universal" = false || continue
+      ;;
     nosideeffect)
       # after this tag, mechanisms are not by side-effect, so they'll
       # only be used when explicitly requested